Unwinding apparatus



Jan. 14, 1969 MIER 3,421,710

UNWIND ING APPARATUS Filed Sept. 27, 1966 Sheet of 4 earner fl: W 5; X5L2 9 m/sm HIS/57095? I UNWINDING APPARATUS I Fi'led Sept. 27, 1966Sheet 2 of 4 C [mm/c \j M0700 Jan. 14, 1969 G. MIER 3,421,110

UNWINDING APPARATUS Filed Sept. 27, 1966 Sheet of 4 Torque Speed 591.

Z z I 7)) Inventor Y n. l v a) //j/ 2? Y I Attorney Jan 14, 1969 MIER3','-4' 21,71o-

UNWINDING APPARATUS Filed Sept. 27, 1966 Sheet 4 of 4 k, 5 K K a 3 SpeedF/g' In uentor 7 h 1A b; 4 c

United States Patent ABSTRACT OF THE DISCLOSURE In controlling thetension of unwinding material, the pole wheel magnet brake is drawn in adirection opposite to that of a reel shaft at a speed which, with thereel shaft stationary, is sufiicient to reach the point of maximumtorque, on the torque-speed characteristic, at the initial value of thebrake coil current; thereafter, in the period between the commencementof unwinding and the attainment of full speed of the unwound materialthe brake coil current is regulated in accordance with the speed of theunwound material so that the current/ speed characteristic for the brakehas a positive slope; and is made zero or negative.

The invention relates to apparatus for controlling the tension in theunwound material in unwinding arrangements employing an electromagneticbrake (induction or eddy-current brake) with an approximately hyperbolictorque-speed characteristic. It is desirable so to control thearrangement that the desired tensile stress of the strip materialremains constant throughout the unwinding operation.

The problem posed in unwinding arrangements generally consists inobtaining as constant a tensile stress as possible irrespective of thewinding diameter. Depending on the nature of the wound material and themanufacturing conditions, the degree of accuracy with which the tensilestress is to be maintained varies considerably.

Control arrangements for electro-magnetic brakes are known which efiectregulation to constant unwinding capacity and keep the tensile stress onthe strip material constant at constant speed of the strip. Onacceleration and deceleration, however, deviations from the desiredstrip tension occur. Such deviations are not permissible in many cases,in particular in the case of easily damaged strip material or when alarge inertial mass is provided by the wound coil.

Furthermore, control or regulating arrangements for unwinders are knownwhich measure the tensile stress of the strip material directly and usethis quantity for regulation purposes. In these arrangements, thetensile stress is kept constant irrespective of the winding diameter andof acceleration and deceleration processes. However, the use of thesestrip tension measuring arrangements leads to additional expenditure forexample for pressure-measuring capsules, tension adjusting rolls orpressure rollers which are additionally undesirable in many cases forreasons of space or because of special surface sensitivity of the stripmaterial. Additionally, control arrangements for electromagnetic brakesare known which regulate strip tension by means of apparatus formechanically or optically scanning the reel diameter. The drawback inthese arrangements also resides in the additional expenditure onconstruction or in a certain hindrance in the operation of the machine.I

The present invention avoids this additional expenditure and thedrawbacks associated therewith and nevertheless produces a substantiallyconstant strip tension throughout the unwinding operation by employingelectromagnetic brakes, known in themselves, of a kind having atorquespeed characteristic which after reaching a maximum torque as thespeed increases from zero falls approximately hyperbolically. Directmeasurement of the tensile stress and the winding diameter isdeliberately avoided. According to the invention, the pole wheel of thebrake is driven in a direction opposite to that of the reel shaft at aspeed which, with the reel shaft stationary, is sufiicient to reach thepoint of maximum torque, on the torque-speed characteristic, at theinitial value of the brake coil current; thereafter, in the periodbetween the commencement of unwinding and the attainment of full speedof the unwound material the brake coil current is regulated inaccordance with the speed of the unwound material so that thecurrent/speed characteristic for the brake has a positive slope; and thecurrent is then either maintained constant with increasing reel speed asthe diameter of the wound material decreases, or the current is reducedas the reel speed increases. An electric signal derived from atachometer connected to draw rollers for withdrawing wound material fromthe reel can be added to a constant signal and then used to control thebrake coil current during the period of running up to full speed of theunwound material.

In order that the invention may be better understood, two examples ofapparatus embodying the invention will now be described with referenceto the accompanying drawings in which:

FIGURE 1 shows the circuit and arrangement of a first apparatus;

FIGURE 2 shows the circuit and arrangement of a second form ofapparatus;

FIGURE 3 shows the torque-speed characteristic of the brake;

FIGURE 4 shows the coil-current/speed characteristic of the controlledbrake;

FIGURE 5 illustrates the resistance curve for the acceleration anddeceleration circuit;

FIGURE 6 shows the coil current/speed characteristic of the brake forthe second form of apparatus.

The strip material is drawn from the winding-off reel 2 by the drivingrollers 1. An electro-magnetic brake 3 (an eddy-current or inductionbrake) is connected to the reel shaft. It consists of two rotatablymounted halves, the socalled pole wheel 3a and the armature. The torqueis transmitted by magnetic force and can be regulated by means of thecurrent in the coil 4. The different values of current strength in thecoil lead to a family of curves for the torque-speed characteristic ofthe electro-magnetic brake. These curves all have a form generallysimilar to that shown in FIGURE 3 and vary only by their ordinates,smaller values of the current corresponding to smaller values of torque.One half of the eddy-current or induction brake is coupled to the reelshaft and the other half is driven at constant speed in the directionopposite to the direction of wind-off by a geared three-phase electricmotor 5. The speed is preferably so calculated that it is located at theturning point of the torque speed characteristic of FIGURE 3, in whichthe speed is the relative speed of the two brake parts. By turning pointthere is to be understood that point at which the upward convexcurvature of the characteristic changes into an upward concavecurvature. As a result, the steeply rising part of the characteristic asfar as the turning point is avoided and only the part which is of anupward concave curvature and which is approximately hyperbolic isfollowed. It is not necessary for the speed to be exactly that requiredfor the turning poin a smaller speed can be used provided that the pointof maximum torque is reached; or a higher speed can be used, but itwould not then be possible to use the full capacity of the brake.

The coil 4 is fed by an amplifier 6. The amplifier contains acurrent-regulating means which compares nominal and actual values andwhich ensures that the coil current is not alfected by the heating ofthe coil and the increase in the ohmic resistance that is associatedtherewith.

Rotary resistors 7, 8 and 9 are located in the input circuit of theamplifier 6. The rotary resistors 7 and 8 are mechanically coupled toone another and are adjusted to the initial winding diameter by means ofa manually-operated rotary knob. The resistor 9 serves to adjust thedesired winding tension and is connected in series with furtherresistors 10, 11, 17 and 18. The series-connected resistors 10 and 11receive the sum of the voltage of a tachometer 12 and constant DC.voltage from a source 13. A tachometer 19 is connected across resistors17 and 18. The tachometer 12 is mechanically coupled to the drivingrollers 1 and its output therefore represents the linear speed of theunwound strip; the tachometer 19 is mechanically coupled to the reelshaft 2.

Even when the unwinding reel 2 is still at rest, there is already arelative speed between the two halves of the induction or eddy-currentbrake (due to the motor so that the tensile stress in the windingmaterial between the driving rollers 1 and the reel 2 can be adjusted tothe desired value with the reel stationary by means of the resistor 9.

If it is assumed that, when the unwinding arrangement starts up anduntil full speed of the strip is reached, the winding diameter decreasesonly to a negligible extent, the braking torque of the induction oreddy-current brake must remain constant in order to obtain a constanttensile stress. Without an adjustment to the current, the increase inrelative speed speed of the two parts of the brake would cause a fall intorque. A constant torque shown as a dashed line parallel to the speedaxis in FIGURE 3 can be achieved by causing the coil current (FIGURE 4)to increase from the value a adjusted at rest to the value b. To thevalue b of the coil-current corresponds the torquespeed characteristicof the brake represented by a full line in FIGURE 3. For the value a ofcoil-current there would be a lower curve (i.e. a curve having lowerordinates) which is not represented in FIGURE 1, and -for which theturning point is at the left-hand end of this dashed line parallel tothe speed axis. Starting from this turning point for current a, thetorque is prevented from decreasmg, as the speed increases, by theincrease in current from a to b. The zero point of FIGURE 4 is displacedrelative to FIGURE 3 so as to be at the abscissa of FIG- URE 3corresponding to the turning point. The characteristic in accordancewith which the adjustment of the coil current must take place can bedetermined point-by-point by graphic methods from the naturaltorque-speed characteristic of the electro-magnetic brake employed. Aslightly curved characteristic (represented by the line a to b in FIGURE4) is obtained, but it is possible to approximate this curve withsufiicient accuracy by a straight line. The manner in which thestraight-line characteristic is obtained will be explained later.

After full speed of the strip has been reached, further unwinding shouldlikewise take place at a constant tension and as the winding diameter isnow decreasing at a greater rate, it is a factor which must beconsidered. The torque is obtained from the product of the tensile forceand the winding radius and must therefore decrease to the same extent asthe winding diameter. At constant strip speed, the result is a variationin torque in inverse ratio to the reel speed, i.e. in accordance with ahyperbola (shown by dashes in FIGURE 3). In order to achieve this, thecoil current of the induction is made to decrease in dependence on thereel speed (FIGURE 4). The characteristic in accordance with which thecoil current must be varied can likewise be determined point-by-point bygraphic methods from the natural torque-speed characteristic of theelectro-magnetic brake employed. An almost linear path is also obtainedfor this part of the current characteristic. In order to obtain thedesired curve for the torque (shown in dashes in FIGURE 3), i.e. aconstant braking torque during the run-up of the unwinder and ahyperbolically decreasing torque during unwinding at constant stripspeed, the coil current of the induction brake must therefore first bemade to increase in dependence on the strip speed and then downwards independence on the reel speed, in accordance with the angledcharacteristic of FIGURE 4.

This angled current characteristic is obtained by the differentialconnection of the two tachometers 12 and 19. The series-connectedtachometer 12 and DC. voltage source 13 apply a voltage acrosspotentiometer 10 and resistor 11 and the tapped voltage corresponds tothe characteristic 1 (FIGURE 4). The DC. voltage is responsible for theinitial value a of the coil current when the reel is at rest. On run-up,the tachometer 12 coupled to the driving rollers delivers a voltagewhich increases in proportion to the speed of the unwound strip andremains constant when full strip speed has been reached (characteristic1, FIGURE 4). The tachometer 19, which is coupled to the reel shaft,delivers a voltage which increases in proportion to the speed of thereel. This voltage is applied across the series-connected resistor 17and resistor 18 and the voltage tapped at the wiper of resistor 17corresponds to the characteristic 2 of FIGURE 2. The negative ends ofthe resistors 11 and 18 are connected together. The difference betweenthe two voltages tapped by the wipers of the resistors 10 and 17 isapplied across the potentiometer 9 and controls the coil current inaccordance with the angled current characteristic (FIGURE 4). Thisdesired current characteristic is thus obtained by the difference of thetwo characteristics 1 and 2 (FIG- URE 4 The initial point a (FIGURE 4)and the slope of the current characteristic are also dependent on theinitial diameter of the winding material. This effect is taken intoconsideration by the resistors 10 and 17. The fixed resistors 11 and 18represent the smallest possible winding diameter, i.e. that of the reelmandrel or shaft.

On acceleration and deceleration of the unwinding arrangement,additional forces occur, these being dependent on the size of theinertial masses and the difference in speed per unit of time. It isassumed that the winding diameter can be regarded as a measure of thetotal inertial moment and that run-up and slowing down take place withconstant acceleration and deceleration, respectively. On acceleration,the switch 24 closes and on deceleration the switch 25 closes. A DC.voltage is applied in each case across the series-connectedpotentiometers 7 and 8, the polarity depending on whether the switch 24or 25 is closed, and the voltage between the wipers of thesepotentiometers varies the current supplied to the coil 4 by way of theamplifier 6 in such a manner that the acceleration and decelerationforces at the reel shaft are compensated. The sense of the correctingDC. voltage derived from the wipers of resistors 7 and 8 must be suchthat this voltage is deducted from the voltage tapped from the resistor9 during acceleration, and is added to this latter voltage duringdeceleration. The switches 24 and 25 open again once the acceleration ordeceleration has ended, these switches being controlled by accelerationand deceleration sensitive devices. FIGURE 5 shows an example of thevaration of resistance required to compensate for acceleration forces independence on the reel diameter. The characteristic first has a negativeslope but as the winding diameter increases, this changes to a positiveslope. Such a characteristic is obtained when the inertial moment of theunwinding mandrel together with the mechanically coupled parts issufliciently large, in relation to the inertial moment of the woundcoil, not to be disregarded.

This characteristic can be approximated by giving the two mechanicallycoupled rotary resistors 7 and 8 a stepped winding such as to producefor each of them a resistance curve (shown in dashes in FIGURE 5)consisting of a number of linear portions of different slopes,

and by so connecting them electrically in series with their wipersmoving in opposition that the sum of the two resistance value, duringprogressive adjustment of the angular position of the wipers firstdecreases and then increases again, so that the resistance curve desiredfor the required acceleration is obtained with good approximation. Theresistor 26 is introduced because of mechanical friction; the frictionalforces at the reel shaft have a braking action and the applieddeceleration voltage value has therefore to be smaller than theacceleration voltage value.

The resistors 7, 8, and 17 are set to the initial diameter of thewinding 0n reel 2 and then remain at this setting throughout theunwinding operation, unless for any reasons the unwinding is stoppedbefore the strip is completely unwound. In such a case, thesepotentiometers would be reset to the new initial diameter.

The apparatus described above provides good compensation for thechanging diameter of the would strip as unwinding proceeds. However,compensation to such a degree of accuracy may not in all cases benecessary and where this is so the simplified apparatus of FIGURE 2 maybe used. This apparatus produces a coil current/ speed characteristic ofthe kind shown in FIGURE 6. It will be seen that in this case, once theunwound strip has attained full speed the coil current remains constant,the approximately hyperbolic torque-speed characteristic of the brakeautomatically providing some compensation for the effect, on the striptension, of the decreasing winding diameter. As in the first case, thespeed of rotation of the pole wheel of the brake is such that with thereel 2 stationary, the turning point of the torque-speed characteristic(or at least the point of maximum torque) is reached. In FIGURE 2, thetachometer 19 of FIGURE 1 is omitted together with the potentiometer 17and the resistor 18 and the potentiometer 9 is supplied with the voltagebetween the wiper of the potentiometer 10' and the negative end of theresistor 11. The apparatus is in other respects similar to that ofFIGURE 1. As a consequence of these changes, the voltage applied acrosspotentiometer 9 varies only with the output of the tachometer 12,superimposed on the constant D.C. voltage from the source 13. Thisprovides the angled current characteristic shown in FIGURE 6.

What I claim is:

1. Apparatus including an unwinding device having a reel for thematerial to be unwound and draw rollers for drawing the material fromthe reel, an eddy-current brake coupled to the reel shaft, means forrotating the pole wheel of the brake in a direction opposite to thedirection of rotation of reel shaft, a tachometer connected to the drawrollers, a DC. voltage source connected in series with the tachometer,and a control circuit applying to the coil of the eddy-current brake acurrent which varies with the sum of the tachometer voltage and the DC.voltage source, in which the control circuit for the coil of the brakeincludes an adjustable resistance to be set in accordance with theintial diameter of the wound material on the reel, the adjustableresistance being connected to the constant DC voltage source through areversing switch which is closed in one sense during acceleration and inthe opposite sense during deceleration of the reel, the decelerationcircuit including an additional resistor.

2. Apparatus in accordance with claim 1, in which the said adjustableresistance comprises two resistors, both set in accordance with theinitial diameter of the wound material, the two resistors beingcontoured to provide a non-linear resistance variation and having theirwipers connected in mechanical opposition so that the sum of theirresistances, plotted against the diameter of the wound material, firstdecreases in non-linear manner as the diameter is reduced and thenincreases, to provide the required acceleration characteristic.

3. An arrangement for maintaining substantially constant the tension inthe wound material in an unwinding device including a reel for thematerial to be unwound and draw rollers for drawing the material fromthe reel, an eddy-current brake coupled with the unwinding shaft andhaving a torque speed characteristic which after reaching a maximumtorque falls approximate-1y hyperbolically with increasing slip, a motorfor driving the pole wheel of the brake in a directon opposite to thatof the reel shaft, a tachometer connected to the draw rollers, a AC.voltage source connected in series with the tachometer, a plurality ofresistors, and wipers therefor in which (a) the free ends of the DC.source and the tachometer connected in series are connected to the endsof a first one of said resistors which (b) is connected by one of itsends and by its 'wiper with both ends of a second resistor, and

(c) one end of the second resistor and its wiper are connected across anamplifier with the winding of the brake pole wheel.

4. Arrangement according to claim 1 in which there is provided a secondtachometer coupled with the unwinding shaft and connected to the ends ofa third resistor which is inserted by one of its ends and its wiper inthe connection between the first resistor and the second resistor,whereby the voltage of the second tachometer is opposed to the sum ofthe voltages produced by the first mentioned tachometer and the D0.source.

5. Arrangement according to claim 1 in which for the compensation of theacceleration and deceleration forces two further resistors arranged inseries are provided for the connection of the second resistor and theamplifier, there are provided wipers for said further resistors, and twoswitches, and a further D.C. source, the further resistors are connectedat their free ends with said further D.C. source across two switches forpole changing.

6. Arrangement according to claim 3, in which a resistor is inserted inseries with the further resistors and the switch to be closed atdeceleration.

7. Arrangement according to claim 3, in which the further resistors arecontoured to provide a non-linear resistance so that the sum of theirresistances as picked up by their wipers mechanically connected withanother, plotted against the diameter of the wound material, firstdecreases in a non-linear manner as the diameter of the supply reel isreduced and then increases, to provide the required accelerationcharacteristic.

8. Arrangement according to claim 3, in which the wipers of theresistors (7, 8, 10 and 17) are mechanically coupled and simultaneouslyadjustable whereby the windings of the potentiometers are accorded witheach other in order to furnish the desired resistance values for eachposition of the wipers.

9. Arrangement according to claim 1, in which each of the first andthird resistors consist of two parts, one of them representing diameterof the core on which the material is wound and the other beingadjustable in function of the initial diameter of the material wound onthe core.

References Cited UNITED STATES PATENTS 2,469,706 5/1949 Winther 1.42-75.51 2,917,252 12/ 1959 Bushnell et a1. 242-75.47 3,049,313 8/1962Jordan et a1. 242-75.44 3,257,086 6/ 1966 Drenning 24275.47 X

FOREIGN PATENTS 544,925 5/ 1942. Great Britain.

FRANK I. COHEN, Primary Examiner.

N. L. MINTZ, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,421,710 January 14, 1969 Gerhard Mier It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 3, line 31, cancel "speed", second occurrence. Column 4, line 27"resistors" should read Potentiometers line 28, potentiometef shouldread resistor Column 5, line 3, "value" should read values line 14,"reasons" should read reason line 18, "would" should read wound Column6, line 11, "A.C. should read D.C. line 22, claim reference numeral "1should read 3 line 30, claimre'ference numeral 1'' should read 3 line38, claim reference numeral "3" should read S line 41, claim referencenumeral "3" should read 5 line 49, claim'reference numeral "3" shouldread 5 line 55 claim reference numeral "1" should read 4 Signed andsealed this 17th day of March. 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

